They are neither locks or flood gates, but gates to keep water in the pond after high tide. The escaping water was then used to run the grist mill. On an incoming tide there was about 2 feet of clearance under the gates. Many of us swam under them, much to the distaste of the lifeguards.

As the tide changed, the gates would close and hold water back, hence the name Mill Pond. The gates were raised yearly to flush out the pond and allow any repair work to be done to the stone coffer dams, and flush out some of the other stuff that would accumulate.

The Mill Pond has gotten a lot shallower over the years, due to sand coming from Compo Cove and the state park. Farmers used to harvest the salt hay that grows on the flats, and the channels were cut for mosquito control. The Mill Pond is one of Westport’s and the state’s true treasures.

It’s the railroad station in Westport NY. I knew it wasn’t the Westport CT RR station. I took a train through Westport NY when I was in college in 1967, returning from a college sponsored trip to Expo in Montreal. A google search proved my hunch to be correct